Forge welding involves circumferential heating of the pipe ends that are to be joined and subsequently pressing the pipe ends together to form a metallurgical bond.
A large variety of heating technologies may be used to make the pipe ends hot enough such that the metallurgical bond can be made. The heating techniques may involve electric, electromagnetic, induction, infrared, arcing and/or friction heating or combinations of these and other heating methods.
When used in this specification the term forge welding is intended to encompass all techniques which involve circumferential heating of pipe ends and subsequent metallurgical bonding of the heated pipe ends, including welding techniques that are generally known as fusion or diffusion welding, friction welding, flash welding and/or butt welding.
It is known from U.S. Pat. Nos. 4,566,625, 4,736,084, 4,669,650, and 5,721,413 issued to Per H. Moe that it may be beneficial to flush the pipe ends just before and during the forge welding operation with a reducing flushing gas, such as hydrogen or carbon monoxide, such that surface oxides are removed from the heated pipe ends and a metallurgical bond with a minimal amount of irregularities is obtained. It is also known from U.S. Pat. Nos. 2,719,207 and 4,728,760 to use non-explosive gas mixtures comprising about 95% by volume of a substantially insert gas, such as argon, nitrogen and/or helium, and about 5% by volume of a reducing gas, such as hydrogen and/or carbon monoxide for flash welding and induction butt welding.
Experiments have shown that forge welding techniques are capable to generate high quality metallurgical bonds between the tubular ends, in particular if the pipe ends are flushed with a reducing gas mixture during the welding operation, but that the red-hot pipe ends are generally deformed such that upsets are formed in the region of the welding zone.
For obtaining a high quality forge weld joint it is required to keep the tubular ends fully aligned with the end faces parallel to each other at a well-defined spacing of a few millimeters only during the heat-up phase and to terminate the heat-up if the pipe ends have reached a preset temperature and to forge the tubular ends for a well-defined length and to cool them down quickly at a well defined cooling rate, which steps are difficult to accomplish at many sites where pipe ends are welded together, such as on oil rigs, pipelaying barges and many on-land sites where underground or above-ground pipelines are to be installed.
Use of EMAT assemblies for inspecting welds is known from, for example, U.S. Pat. Nos. 5,439,157 and 5,474,225. In the known EMAT weld inspection methods a robotic transport apparatus containing EMAT transmitting and receiving coils is automatically positioned at one side of a just-completed weld whereupon the EMAT transmitting coil transmits ultrasonic SH shear waves towards the weld and the EMAT receiving coil transduces any ultrasonic SH shear waves reflected by the weld in a signal which is used to signal the presence of defects in the weld on the basis of the received signal. The robotic transport apparatus is in use moved along the surface of one of the welded plates parallel to the weld and may be connected to a control unit which automatically adjusts the settings of the welding apparatus which moves ahead of the EMAT weld assembly. The use of a robotic transport apparatus is not practical for inspection of welds between tubulars since it requires the robotic transport apparatus to rotate around a welded tubular, which is time consuming and requires the use of a fragile robotic tool.
The use of EMAT devices for weld and/or pipe inspection is also disclosed in U.S. Pat. No. 5,652,389 to Barnes, et. al., U.S. Pat. No. 5,760,307 to Latimer et. al., WO Patent No. 02/40986 and U.S. Pat. No. 5,808,202 to Passarelli. Barnes discloses a pulse-echo technique and apparatus for inspection of inertia welds in plat-plates using EMAT. Latimer discloses a method to eliminate root and crown signals using crossed or collinear EMATs, and Passarelli discloses a pulse-echo technique for the inspection of cylindrical objects including rods and tubes.
The device disclosed by Passarelli has the disadvantage that it is has a fixed ring-shape construction, which cannot be put readily around the tubulars and the weld at the rig floor without the danger of damaging the device or at the expense of substantial time delays. Another disadvantage to this arrangement is the geometry of the electromagnets, the transmitter and the receiver coil, which does not provide a 100% inspection of the weld around the circumference of the pipe, as the aperture of the transmitters is smaller than the ultrasonic field at the weld region. Rotating the tubular could mitigate the disadvantage, but that is not possible when the tubulars are welded at the rig floor, as will be explained below. An additional, difficulty posed by this and other prior art is that the weld is inspected by pulse-echo reflection measurement only. However, to prevent miss-interpretation of the reflected signals, e.g. due to diffraction or scatter at the weld, it is preferred to measure both reflection and transmission at the same time using at least two EMATs positioned upstream and downstream from the weld.
Expandable tubulars are increasingly used in oil and gas production wells and may comprise slots or other perforations which are widened as a result of the expansion or may have a continuous ‘un-slotted’ wall which is circumferentially stretched by an expansion device such as an expansion cone and/or a set of rollers.
Expandable tubulars are generally joined by mechanical connectors since welding may create at least some strengthening and/or weakening of the pipe wall in the region of the weld, and strengthening will hamper or even disrupt the expansion process whereas weakening will result in a tube which will easily collapse, buckle and/or burst in the welding zone.
In addition, here it is required to weld slotted liners there are particular problems to overcome. In the first instance slotted expandable tubulars are difficult to seal completely to allow flushing with non-oxidising or reducing gases or gas mixtures and removal of air. In the second place welding the end of unprepared slotted liners will also cause the slots at the end of the tubular to be welded also. This impedes expansion and prevents proper functioning of the slotted expandable tubular.
It is known from International patent application WO 98/33619 to connect expandable tubulars by amorphous bonding and from International patent application WO 0230611 to connect expandable tubulars by laser welding. However these connection techniques are time consuming and require a very precise positioning of the pipe ends relative to each other and machining the pipe ends into an extremely accurate flat shape that these technologies are not practical for use on for example a drilling rig, an offshore oil platform or pipe laying vessel.
When pipes are joined and used in for example a downhole, sub-sea or remote environment it is advantageous to log the position of individual pipes or to detect the position of individual pipes when the pipe and/or surrounding hole is re-entered. This is useful to e.g. allow accurate placement of side-tracks, packers and perforations. Logging of this nature is done by measuring the distance a tool has travelled within or adjacent to the pipe, counting the number of connections or by positioning easily identifiable markers, such as magnetic or radioactive markers, in the hole alongside, and attached to, the pipe, which may be a production tubing and/or casing which marker may be found using specialized equipment. In addition special pup joints are often used for this purpose. The existing methods for marking pipe joints are expensive, time consuming and may lead to a quick wear of the markings and replacement of worn markings may require retrieval of the entire pipe string from a well, which is very expensive.